Meet 1
Congratulations!
The first meeting is a brilliant experience!
Lots of first meets are scheduled for less than 5 people (ours was for 2) so don't worry about numbers.
In fact don't worry about anything, just arrange a location, publicize it for a few weeks, and try to get there on time.
Add it to the http://php.net/ calendar, and any local tech events calendars.
The rest just happens and you can take it from there.
The intros and common denominators such as companies, people, jobs etc. take up a good chunk of the first evening.
If you feel the need for topics suggest a topic or two to start with. If you are meeting in a public place make sure no one can miss you (probably quite unlikely) But a sign on the table or door can do wonders.
A good note to finish on before people start to leave is to briefly discuss the next meeting date, location etc. Yes this can be done online but face to face has its advantages too.